The present invention relates to a connecting piece for establishing a connecting arrangement which can be pressed together, having a stub which can be inserted into a pipe and on which profilings are provided for the pressing-together with the pipe and which can be pushed into the pipe to a stop. 
In the prior art, supporting pipes constructed as a connecting piece were suggested, which supporting pipes are pushed into a pipe for establishing a pressed connection. For this purpose, the supporting pipe has a stub whose outer circumference corresponds approximately to the inner circumference of the pipe. For establishing a pressed connection, a pressure sleeve is placed around an end section of the stub and this pressure sleeve is then pressed onto the pipe so that the pipe made of a plastic or a composite material is durably held against the supporting pipe in a pressed manner in order to obtain a secure sealing. Such supporting pipes and connecting arrangements have the disadvantage that, after the sliding-in of the stub of the supporting pipe, a preliminary sealing between the pipe and the stub can be obtained so that a preliminary sealing is achieved even without a pressed connection. However, after a short time, an unintentional leakage may result. This effect is intensified when a receiving device for a sealing ring is arranged on the stub. The sealing ring, after the sliding-in, then provides a sealing with the pipe. 
It is therefore an object of the invention to provide a connecting piece for establishing a connecting arrangement which can be pressed together, where forgetting to press the connection together can be recognized immediately in that no sealing exists between the connecting piece and the pipe in the not-pressed-together condition and, when the connection is tested, a fluid or air will leak out. A durable sealing should be achieved only after the pressing-together.  
This object is achieved by a connecting piece as well as a corresponding connecting arrangement of the present invention. 
According to the invention, at least one radially projecting spacer is provided on the stub, the spacer defining a gap for forming a flow duct between the stub and the pipe. The stub therefore has a slightly smaller circumference, so that a slight gap is provided between the stub and the pipe through which, in the not-pressed-together condition, a fluid or air contained in the pipe can flow out. This immediately indicates that it was forgotten to press the connection together. In this case, the spacer has the function of defining the gap, in which case the connecting piece may also be arranged on the spacer with a certain clamping in order to reach a prefixing of the pipe to the stub. In addition, the stub with the pressable section may be constructed to be essentially circular on the circumference, so that known pressing tools with round cheek plates can be used for the pressing-together. To this extent, the pressing operation does not change for the fitter. In particular, the pressing-together can take place independently of a possible rotation of the connecting piece in the pipe. Also, manufacturing tolerances of the pipe and of the supporting body play a subordinate role for this function. 
According to a preferred embodiment, adjacent to the spacer, the stub has a section which can be pressed together and has an essentially ring-shaped cross-section. Thus, when known pressing tools with round cheek plates are used, a uniform contact pressure is obtained in the area of the pressed section. The uniform pressure on the stub permits a minimizing of the stressing of the material on the pipe and the stub. 
Preferably, a first spacer is provided on the stub on an end section and a second spacer is provided adjacent to the stop. As a result, the gap formed between the pipe and the stub is fixed on two opposite ends, so that an essentially circular circumference of the stub can be provided in the center in the area to be pressed together. As a result of the two-sided support, when the pipe is inserted with a certain prestressing—thus, when the pipe experiences a slight bending—, a leakiness nevertheless exists as a result of the gap  because the pipe is largely fixed along the length of this stub and can experience only very slight bendings. However, the gap is not closed off as a result of such bendings. 
The preferred shape of the spacers is such that these have an at least partially ring-shaped construction and have at least one interruption for forming a flow duct between the stub and the pipe. An essentially ring-shaped construction of the spacers permits a truly axial fixing of the stub inside the pipe. However, it is also possible to provide different spacers, such as knobs, strip-shaped enlargements, projections extending longitudinally with respect to the axis of the stub, diagonally extending projections or ribs. It is only required that the spacers fix a gap between the remaining stub and the pipe. 
In order to obtain a durable pressed connection secured against displacements, a pressable section is preferably provided on the stub. The section has a plurality of ribs which are circular on the outer circumference. As a result, the material of the pipe can dig into the ribs, and relative movement between the stub and the pipe after the pressing-together is avoided. 
According to another embodiment of the invention, a recess for forming a flow duct between the face of the pipe and the stop is provided on the stop of the connecting piece. The intention is that, when the pressing-together has been forgotten and the pipe system is connected, a fluid or air can flow out between the pipe and the stub. An unintentional sealing may even also take place when the pipe rests loosely with its entering edge against a plane stop of the connecting piece. In order to therefore ensure that a premature sealing by the entering edge and the stop of the pipe does not take place even accidentally, at least one recess is preferably provided for forming a flow duct because this recess cannot be closed off even accidentally. 
In order to achieve a durable sealing of the pressed-together connecting arrangement, a ring-shaped recess for receiving a sealing ring is preferably provided on the stub. In this case, the connecting piece may be made of metal or of a plastic material. 
According to the invention, a connecting arrangement is also provided in which a corresponding connecting piece with a stub is pushed into a pipe. In order  to obtain a durable deformation of the stub, a pressure sleeve is preferably provided around the end section of the pipe. The pressure sleeve may be held by a holding ring in a prefixed manner on the connecting piece, so that the pressure sleeve, the holding ring and the connecting piece form a preassembled unit. Instead of a supporting sleeve, the pipe may also be constructed of metal and may be pressed directly onto the stub of the connecting piece. 
In the following, the invention will be explained in detail by means of an embodiment with reference to the attached drawings. 